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Kernel: Implement lazy committed page allocation
By designating a committed page pool we can guarantee to have physical pages available for lazy allocation in mappings. However, when forking we will overcommit. The assumption is that worst-case it's better for the fork to die due to insufficient physical memory on COW access than the parent that created the region. If a fork wants to ensure that all memory is available (trigger a commit) then it can use madvise. This also means that fork now can gracefully fail if we don't have enough physical pages available.
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20 changed files with 329 additions and 67 deletions
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@ -110,6 +110,9 @@ public:
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Yes
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};
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bool commit_user_physical_pages(size_t);
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void uncommit_user_physical_pages(size_t);
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NonnullRefPtr<PhysicalPage> allocate_committed_user_physical_page(ShouldZeroFill = ShouldZeroFill::Yes);
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RefPtr<PhysicalPage> allocate_user_physical_page(ShouldZeroFill = ShouldZeroFill::Yes, bool* did_purge = nullptr);
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RefPtr<PhysicalPage> allocate_supervisor_physical_page();
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NonnullRefPtrVector<PhysicalPage> allocate_contiguous_supervisor_physical_pages(size_t size);
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@ -155,6 +158,7 @@ public:
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void dump_kernel_regions();
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PhysicalPage& shared_zero_page() { return *m_shared_zero_page; }
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PhysicalPage& lazy_committed_page() { return *m_lazy_committed_page; }
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PageDirectory& kernel_page_directory() { return *m_kernel_page_directory; }
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@ -185,7 +189,7 @@ private:
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static Region* find_region_from_vaddr(VirtualAddress);
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RefPtr<PhysicalPage> find_free_user_physical_page();
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RefPtr<PhysicalPage> find_free_user_physical_page(bool);
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u8* quickmap_page(PhysicalPage&);
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void unquickmap_page();
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@ -200,9 +204,12 @@ private:
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RefPtr<PhysicalPage> m_low_page_table;
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RefPtr<PhysicalPage> m_shared_zero_page;
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RefPtr<PhysicalPage> m_lazy_committed_page;
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unsigned m_user_physical_pages { 0 };
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unsigned m_user_physical_pages_used { 0 };
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unsigned m_user_physical_pages_committed { 0 };
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unsigned m_user_physical_pages_uncommitted { 0 };
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unsigned m_super_physical_pages { 0 };
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unsigned m_super_physical_pages_used { 0 };
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@ -250,4 +257,9 @@ inline bool PhysicalPage::is_shared_zero_page() const
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return this == &MM.shared_zero_page();
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}
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inline bool PhysicalPage::is_lazy_committed_page() const
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{
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return this == &MM.lazy_committed_page();
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}
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}
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